1. Field of the Invention
This invention lies in the field of cardiac pacing apparatus and, more particularly, in the area of electrodes, or catheters, used in a cardiac pacing system, for delivering stimulating signals generated by an electronic pacer to the heart.
2. Description of the Prior Art
This specification discloses an electrode as used in cardiac pacing. In much of the literature, the term catheter is employed to describe the same apparatus. For example, the electrode of this invention may also be suitably described as a unilateral catheter having a single electrode, in which description the term electrode would refer to the stimulating tip. In this specification, the term electrode is used with the same meaning as catheter, referring to the entire device for conducting stimulating pulses.
A chronic problem with electrodes as used in cardiac pacing is proper fixation of the distal tip within the heart so that good contact is made with the inner lining of the heart, which is necessary to provide good pacing. The term fixating is used to describe the procedure of fixing the electrode tip relative to the inner lining of the heart so that proper stimulation is assured with reasonable permanency. In the case of ventricular pacing, it is known that the stimulating contact element cannot be loosely positioned within the ventricle, but must be fixed against or at least within a minimum distance from the endocardium. Another important reason for obtaining good fixation is so that the threshold for stimulation remains substantially constant throughout the lifetime of electrode usage. Clearly, if the distal stimulating contact is permitted to shift in position relative to the endocardium, the threshold will likewise shift, with potentially disasterous results.
In the prior art, a large number of fixation type designs have been utilized, generally with indifferent success. In some endocardial electrodes, the design is such that the blood can work itself into the electrode and thus block the fixation mechanism. Another disadvantage of most fixation systems is that they pierce or grasp the endocardium so as to cause physical damage. This is particularly serious for atrial electrodes, due to the thin atrial walls. There exist a number of issued patents describing electrodes designed to screw into the heart tissue. However, there has remained a great need in this art for an endocardial catheter which can be safely and securely positioned so as to provide the physician with means for obtaining an optimally low threshold, and which will minimize damage to the endocardium both at time of insertion and later.